The gene product of avian sarcoma virus (ASV) which is responsible for malignant transformation of cells has been identified as a 60,000 MW cytoplasmic phosphoprotein (termed pp60src) which functions as a protein kinase. Normal avian and mammalian cells contain a protein (termed pp60sarc) which is antigenically, structurally, and functionally similar to this protein. The projects proposed in this application involve investigations of the functional expression of these two related proteins. The objective of these studies is to determine which cellular processes the normal cell sarc protein is involved with. Because of the close relationship between this protein and the viral src protein, these studies should be valuable in elucidating the mechanism of src-mediated transformation. The synthesis, processing, and enzymatic activity of the normal cell sarc protein, pp60sarc, will be analyzed in various tissues at different stages of development. These studies will be correlated with investigations of the expression of the viral src protein in tissues which differ in their susceptibiliity to ASV-induced tumorigenesis. Lastly, studies will be performed on the interaction of the viral src protein with a cellular protein with which it is associated in ASV-transformed cells.